Recently, with an increasing integration degree of a semiconductor device, the dimensions of individual elements have become finer, and the widths of wiring and gates constituting each element have also become finer.
An electron beam lithography technique that supports such reduction in the dimensions of elements includes a step of applying a resist composition on a surface of a substrate through a light shielding film, a step of transferring a predetermined pattern by irradiating an electron beam to form a latent image of the pattern in the resist, a step of heating the substrate as necessary, a step of developing the resist to form a desired fine pattern on the substrate, and a step of processing such as etching the light shielding film using the fine pattern as a mask.
The electron beam lithography technique inherently provides a superior resolution, since it uses an electron beam, which is a charged particle beam. For this reason, the electron beam lithography technique has been used in the production of a mask for state-of-the-art semiconductor devices typified by DRAM (Dynamic Random Access Memory).
Japanese Laid-Open Patent Publication No. 1999-312634 discloses a method for producing a semiconductor integrated circuit apparatus using an electron beam lithography technique.
As disclosed in Japanese Laid-Open Patent Publication No. 2011-171497, the aforementioned resist plays an important role in the electron beam lithography technology. For example, a chemical amplification resist has been generally used in the recent electron beam lithography technology. When an unnecessary portion is removed from a resist film formed on a substrate using a reaction caused by an electron beam, a patterned resist film is formed on the substrate. By using the patterned resist film, processing is performed on the substrate.
As mentioned above, the resist plays an important role in the electron beam lithography technology. In recent years, in order to cope with reduction in dimensions of elements, considerations are being made regarding enhancement of resolution of a resist, improvement of roughness of line edges of a resist pattern, control of sensitivity of a resist, or the like. In particular, investigation into controlling a sensitivity of a resist so as to improve accuracy of critical dimension (CD) of a pattern has been conducted.
For example, in order to enhance throughput in a conventional electron beam lithography technology, a high-sensitivity resist of which the sensitivity is equal to or less than 10 μC./cm2 has been used. However, with the enhancement of CD accuracy required in a pattern, the sensitivity of a resist is lowered to 20 μC./cm2 to 30 μC./cm2. In addition, since writing throughput is largely enhanced by adopting multi-beam technology which uses a plurality of electron beams for writing, it makes it possible to further lower the sensitivity of the resist. Specifically, it is possible to perform writing without lowering the throughput even in a state in which the sensitivity is equal to or less than 50 μC./cm2. By lowering the sensitivity of the resist, a variation in CD due to the blur of the beam can be reduced, and as a result, CD accuracy can be improved.
However, lowering of the sensitivity of the resist causes a time for a writing step to be lengthened, and therefore, the throughput of electron beam writing is reduced.
In this case, as a pattern to be written on one substrate, there is a pattern in which high writing accuracy of nanometer (nm) order is required in order to correspond to a reduction of the dimensions of the elements. Also, the pattern to be written generally includes a pattern of which required writing accuracy is not so high, in addition to the above pattern. As one example, the required writing accuracy of a barcode pattern or an ID chip pattern made of a number, a symbol or the like, having a wide writing area, is not so high. For example, writing accuracy of a micrometer order (μm) is required.
Therefore, there is a need for technology of improving CD accuracy by using a resist of which the sensitivity is controlled to be low in a pattern requiring high accuracy and enhancing throughput of writing by using a high-sensitivity resist in a pattern not requiring high accuracy, with respect to one substrate in which a pattern is transferred. The technology can be achieved by arranging a low-sensitivity resist film in a region in which a pattern requiring high accuracy is formed and a high-sensitivity resist film in a region in which a pattern not requiring high accuracy is formed on one substrate.
In the case of performing writing of a pattern requiring high accuracy using the electron beam lithography technology, high flatness is required for a surface of a resist film to be used. Specifically, it is required that a difference between the thickest portion and the thinnest portion of the resist film is within a range of 1 μm to 2 μm, preferably equal to or less than 0.5 μm. In addition, a task in the future is to reduce the difference to be equal to or less than 0.1 μm.
In order to achieve the above-mentioned flatness of the surface of a resist film, it is necessary to adopt a spin coating method suitable for formation of a film having high flatness of the surface.
However, as is well known in the art, in the case where a resist is applied to a substrate in which a pattern is transferred using the spin coating method, it is usual that only one type of resist film is formed on the entire surface of one side of the substrate. Therefore, it is hard to arrange a resist film with an optimal sensitivity in each of a plurality of regions into which the substrate is virtually divided, by the spin coating method.
On the other hand, as a method for forming resist films having different sensitivities respectively in the plurality of regions resulting from virtual division, a method using an inkjet method can be considered.
However, according to a method for coating a resist by the inkjet method, a large height difference is caused between dots formed by supply of a resist. Therefore, it is hard to form a resist film having the flatness of the surface suitable for formation of a pattern requiring high accuracy. That is, a difference between the thickest portion and the thinnest portion in a resist film formed by the inkjet coating method is hardly within the aforementioned range and it is hard to perform writing of a pattern requiring high accuracy.
As described above, there is a need for technology of arranging one type of resist film having an optimal sensitivity and a high flatness of the surface in each of a plurality of regions into which one substrate in which a pattern is transferred is divided according to the accuracy required of a pattern to be written. In such technology, it is necessary to use a spin coating method suitable for formation of a resist film having high flatness of the surface. The present invention has been made in view of these points. That is, an object of the present invention is to provide a method for forming a resist film for forming one optimal type of resist film respectively in a plurality of regions of which the number is two or more, on one substrate by the spin coating method.
Also, an object of the present invention is to provide a method for forming a resist film for forming one optimal type of resist film respectively in a plurality of regions of which the number is two or more, on one substrate by the spin coating method and performing writing with high efficiency using a charged particle beam.
Other challenges and advantages of the present invention are apparent from the following description.